FORMING PLASTICS BY BENDING

Question 0

What is the process of heating or softening plastics known as?

Answer 0

LOCAL heating because it is confined to one part or area of a surface.

Question 1

How can plastics be bent?

Answer 1

By heating and softening just part of a larger piece

Question 2

What is the most common method of forming by local heating known as?

Answer 2

LINE BENDING

Question 3

Explain LINE BENDING - 2 points

Answer 3

1. A plastic sheet is laid over a strip heater which warms up and eventually softens a narrow strip of material.
2. When hot enough, the strip becomes pliable and enables the sheet to be bent.

Question 4

Name two thermoplastic materials which can easily be formed by line bending

Answer 4

1. Polystyrene

2. Acrylic

Question 5

Give the steps in forming a plastic sheet - 3 points

Answer 5

1. Mark out positions of the bend(s) with a pencil or felt-tip
2. Place the marked-out material on the heater until it is pliable - thicker sheets should be turned over and heated from both sides
3. Quickly fold the sheet, if possible against a wooden mould for accuracy

Question 6

What will happen if you overheat the acrylic?

Answer 6

It will start to break down and bubble

Question 7

What does the radius of the bend depend on?

Answer 7

A number of things:

1. The THICKNESS and type of material
2. The LENGTH of time left on the heater - the radius of the bend will increase if the sheet is heated longer, because heat will be conducted through the material, increasing the width of the softened stip.
3. The DISTANCE of the sheet from the heat source

Question 8

What will happen if thicker sheets are folded very tightly?

Answer 8

The outside surface may crack

Question 9

Why will the radius of the bend be increased if the sheet is heated longer?

Answer 9

Because the heat will be conducted through the material, increasing the width of the softened strip

Question 10

If the sheet is at a big distance from the heat source, what will happen?

Answer 10

The sheet will warm up more slowly if it is further from the heat source, but the heat will be spread over a greater width.

Question 11

What can a hot air gun be used for?

Answer 11

To heat thin sheet plastics such as polystyrene and ABS locally. The plastic NOT to be heated is shielded behind weighted plywood sheets. Thick gloves must be worn.